The impact of fresh gas flow on wash-in, wash-out time and gas consumption for sevoflurane and desflurane, comparing two anaesthesia machines, a test-lung study

The effect of different flow levels and concentrations of sevoflurane during the wash-in phase on volatile agent consumption: a randomized controlled trial

PURPOSE

The standard procedure for low-flow anesthesia usually incorporates a high fresh gas flow (FGF) of 4-6 L/minute during the wash-in phase. However, the administration of a high FGF (4-6 L/min) increases the inhaled anesthetic agent consumption. This study was designed to compare the sevoflurane consumption at 2 rates of flow and vaporizer concentration during the wash-in period.

METHODS

Patients were randomly enrolled into high FGF (HFGF) (n = 30) and low FGF (LFGF) (n = 30) groups. During the wash-in, the HFGF group received 4 L/minute FGF with a sevoflurane vaporizer setting of 2.5%, and the LFGF group received 1 L/minute FGF with a vaporizer setting of 8%. Once the wash-in was complete, anesthesia maintenance was performed with 0.5 L/min FGF with a vaporizer setting of 2.5-4.5% in both groups. The patient demographic data, bispectral index values, hemodynamic variables, wash-in time, sevoflurane consumption during the wash-in phase, and total sevoflurane consumption were analyzed.

RESULTS

The median sevoflurane consumption in the wash-in phase was 8.2 mL (7.1-9.3) in the HFGF group and 2.7 mL (2.2-3.1) in the LFGF group (p = 0.001). The mean total sevoflurane consumption was 17.41 ± 3.58 mL in the patients who received HFGF and 14.93 ± 3.57 mL in the LFGF group (p = 0.001). The mean wash-in completion time was 12.49 ± 2.79 min in the HFGF group and 3.35 ± 0.67 min in the LFGF group (p = 0.001).

CONCLUSIONS

The anesthetic agent consumption during the wash-in phase was approximately 3 times lower with the administration of sevoflurane at 1 L/minute FGF than the use of 4 L/minute FGF.

The Relationship between the Timing of Sugammadex Administration and the Upper Airway Obstruction during Awakening from Anesthesia: A Retrospective Study

Background and Objectives: The harmonization of recovery of consciousness and muscular function is important in emergence from anesthesia. Even if muscular function is recovered, tracheal extubation without adequate recovery of consciousness may increase the risk of respiratory complications. In particular, upper airway obstruction is one of the common respiratory complications and can sometimes be fatal. However, the association between the timing of sugammadex administration and the upper airway obstruction that can occur during awakening from anesthesia has rarely been studied. Materials and Methods: The medical records of 456 patients who had surgery under general endotracheal anesthesia (GETA) at the Haeundae Paik Hospital between October 2017 and July 2018 and who received intravenous sugammadex to reverse rocuronium-induced neuromuscular blockade were analyzed. The correlations between bispectral index (BIS) and minimum alveolar concentration (MAC) at the time of sugammadex administration, the incidence of complications, and the time to tracheal extubation were analyzed to investigate how different timings of sugammadex administration affected upper airway obstruction after tracheal extubation. Conclusions: The effect of BIS and the duration from anesthetic discontinuation to sugammadex administration on upper airway obstruction was not statistically significant. However, the odds ratio of complication rates with MAC < 0.3 compared with MAC ≥ 0.3 was 0.40 (95% confidence interval 0.20 to 0.81, p = 0.011), showing a statistically significant increase in risk with MAC ≥ 0.3 for upper airway obstruction.

In vitro performance evaluation of AnaConDaTM-100 and AnaConDaTM-50 compared to a circle breathing system for control and consumption of volatile anaesthetics

To identify the better volatile anaesthetic delivery system in an intensive care setting, we compared the circle breathing system and two models of reflection systems (AnaConDa™ with a dead space of 100 ml (ACD-100) or 50 ml (ACD-50)). These systems were analysed for the parameters like wash-in, consumption, and wash-out of isoflurane and sevoflurane utilising a test lung model. The test lung was connected to a respirator (circle breathing system: Aisys CS™; ACD-100/50: Puriton Bennett 840). Set parameters were volume-controlled mode, tidal volume-500 ml, respiratory rate-10/min, inspiration time-2 sec, PEEP-5 mbar, and oxygen-21%. Wash-in, consumption, and wash-out were investigated at fresh gas flows of 0.5, 1.0, 2.5, and 5.0 l/min. Anaesthetic target concentrations were 0.5, 1.0, 1.5, 2.0, and 2.5%.  Wash-in was slower in ACD-100/-50 compared to the circle breathing system, except for fresh gas flows of 0.5 and 1.0 l/min. The consumption of isoflurane and sevoflurane in ACD-100 and ACD-50 corresponded to the fresh gas flow of 0.5-1.0 l/min in the circle breathing system. Consumption with ACD-50 was higher in comparison to ACD-100, especially at gas concentrations > 1.5%. Wash-out was quicker in ACD-100/-50 than in the circle breathing system at a fresh gas flow of 0.5 l/min, however, it was longer at all the other flow rates. Wash-out was comparable in ACD-100 and ACD-50. Wash-in and wash-out were generally quicker with the circle breathing system than in ACD-100/-50. However, consumption at 0.5 minimum alveolar concentration was comparable at flows of 0.5 and 1.0 l/min.

1-1-8 one-step sevoflurane wash-in scheme for low-flow anesthesia: simple, rapid, and predictable induction

Background

Sevoflurane is suitable for low-flow anesthesia (LFA). LFA needs a wash-in phase. The reported sevoflurane wash-in schemes lack simplicity, target coverage, and applicability. We proposed a one-step 1-1-8 wash-in scheme for sevoflurane LFA to be used with both N₂O and Air. The objective of our study was to identify time for achieving each level of alveolar concentration of sevoflurane (F_AS) from 1 to 3.5% in both contexts.

Methods

We recruited 199 adults requiring general anesthesia with endotracheal intubation and controlled ventilation—102 in group N₂O and 97 in group Air. After induction and intubation, a wash-in was started using a fresh gas flow of O₂:N₂O or O₂:Air at 1:1 L·min^− 1 plus sevoflurane 8%. The ventilation was controlled to maintain end-tidal CO₂ of 30–35 mmHg.

Results

The rising patterns of F_AS and inspired concentration of sevoflurane (F_IS) are similar, running parallel between the groups. The F_AS/F_IS ratio increased from 0.46 to 0.72 within 260 s in group N₂O and from 0.42 to 0.69 within 286 s in group Air. The respective time to achieve an F_AS of 1, 1.5, 2, 2.5, 3, and 3.5% was 1, 1.5, 2, 3, 3.5, and 4.5 min in group N₂O and 1, 1.5, 2, 3, 4, and 5 min in group Air. The heart rate and blood pressure of both groups significantly increased initially then gradually decreased as F_AS increased.

Conclusions

The 1-1-8 wash-in scheme for sevoflurane LFA has many advantages, including simplicity, coverage, swiftness, safety, economy, and that it can be used with both N₂O and Air. A respective F_AS of 1, 1.5, 2, 2.5, 3, and 3.5% when used with N₂O and Air can be expected at 1, 1.5, 2, 3, 3.5, and 4.5 min and 1, 1.5, 2, 3, 4, and 5 min.

Trial registration

This study was retrospectively registered with ClinicalTrials.gov (NCT03510013) on June 8, 2018.

Minimal flow anesthesia can be initiated early with the use of higher fresh gas flow to facilitate desflurane "Wash-in"

Background and Aims:

More than 80% of delivered anesthetic gases get wasted at high fresh gas flows as they are vented out unused. Use of minimal flow anesthesia is associated with less waste anesthetic gas emission and environmental pollution. There is no approved or validated technique to initiate minimal flow anesthesia and simultaneously achieve denitrogenation of the breathing circuit. We studied the wash-in characteristics of desflurane, when delivered with 50% nitrous oxide, to reach a target end-tidal concentration at two different gas flow rates.

Material and Methods:

Patients were allocated randomly to two groups of 25 adults each. In Group A, with the vaporizer dial fixed at 4 vol %, after an initial fresh gas flow of 4 L/min was administered to wash-in of desflurane using the closed-circuit, with 50% N₂O in O₂, and in group B, 6 L/min was used. Minimal flow anesthesia, with 0.5 L/min, was initiated in both groups on attaining a target end-tidal desflurane concentration of 3.5 vol %. After initiation of desflurane delivery, the inspired/expired gas concentrations were noted every minute for 15 min.

Results:

In Group A, the target desflurane end-tidal concentration was reached in 499.2 ± 68.6 s±, and in the Group B (P < 0.001), it was reached significantly faster in 314.4 ± 69.89 s. Denitrogenation of the circuit was adequate in both groups.

Conclusion:

Minimal flow anesthesia can be initiated, without any gas-volume deficit, in about 5 min with an initial fresh gas flow rate of 6 L/min and the vaporizer set at 4 vol%.

Isocapnic hyperventilation provides early extubation after head and neck surgery: A prospective randomized trial

BACKGROUND

Isocapnic hyperventilation (IHV) shortens recovery time after inhalation anaesthesia by increasing ventilation while maintaining a normal airway carbon dioxide (CO2)-level. One way of performing IHV is to infuse CO2 to the inspiratory limb of a breathing circuit during mechanical hyperventilation (HV). In a prospective randomized study, we compared this IHV technique to a standard emergence procedure (control).

METHODS

Thirty-one adult ASA I-III patients undergoing long-duration (>3 hours) sevoflurane anaesthesia for major head and neck surgery were included and randomized to IHV-treatment (n = 16) or control (n = 15). IHV was performed at minute ventilation 13.6 ± 4.3 L/min and CO2 delivery, dosed according to a nomogram tested in a pilot study. Time to extubation and eye-opening was recorded. Inspired (FICO2) and expired (FETCO2) CO2 and arterial CO2 levels (PaCO2) were monitored. Cognition was tested preoperatively and at 20, 40 and 60 minutes after surgery.

RESULTS

Time from turning off the vapourizer to extubation was 13.7 ± 2.5 minutes in the IHV group and 27.4 ± 6.5 minutes in controls (P < .001). Two minutes after extubation, PaCO2 was 6.2 ± 0.5 and 6.2 ± 0.6 kPa in the IHV and control group respectively. In 69% (IHV) vs 53% (controls), post-operative cognition returned to pre-operative values within 40 minutes after surgery (NS). Incidences of pain and nausea/vomiting did not differ between groups.

CONCLUSIONS

In this randomized trial comparing an IHV method with a standard weaning procedure, time to extubation was reduced with 50% in the IHV group. The described IHV method can be used to decrease emergence time from inhalation anaesthesia.

The impact of fresh gas flow on wash-in, wash-out time and gas consumption for sevoflurane and desflurane, comparing two anaesthesia machines, a test-lung study

Low-flow anaesthesia is considered beneficial for the patient and the environment, and it is cost reducing due to reduced anaesthetic gas consumption. An initial high-flow to saturate the circle system ( wash-in) is desirable from a clinical point of view. We measured the wash-in and wash-out times (time to saturate and to eliminate the anaesthetic agent, AA), for sevoflurane and desflurane, in a test-lung with fixed 3 MAC vaporizer setting at different fresh gas flow (FGF) and calculated the consumption of AA. We tried to find an optimal flow rate for speed and gas consumption, comparing two anaesthesia machines (AMs): Aisys and Flow-i. Time to reach 1 minimal alveolar concentration (MAC) (wash-in) decreased (p<0.05) at higher flow rates (1 – 2 – 4) but plateaued at 4-4.8 l/min. The consumption of AA was at its lowest around 4-4.8 l/min (optimal flow) for all but the Aisys /desflurane group. Wash-out times decreased as FGF increased, until reaching plateau at FGF of 4-6 l/min. Aisys had generally shorter wash-in times at flow rates < 4 l/min as well as lower consumption of AA. At higher flow rates there were little difference between the AMs. The “optimal FGF” for wash-out, elimination of gas from the test-lung and circle system, plateaued with no increase in speed beyond 6 l/min. A fresh gas flow of 4 l/min. seems “optimal” taking speed to reach a 1 MAC ET and gas consumption into account during wash-in with a fixed 3 MAC vaporizer setting, and increasing fresh gas flow beyond 6 l/min does not seem to confirm major benefit during wash-out.